The present invention relates to a magneto-optical recording/reproducing method, a disc recording medium, and a magneto-optical recording/reproducing apparatus making use of magnetic field modulation and domain wall displacement detection, or magnetic amplifying magneto-optical system technology.
Optical discs and magneto-optical discs have gained widespread acceptance as disc recording media today, even as diverse techniques for mass data storage on these discs are being developed. One such mass storage technique involves narrowing the track pitch so as to increase recording density in the radial direction on the disc.
One way to reduce the track pitch is by having recourse to so-called land and groove recording whereby data are recorded to both grooves and lands on the disc. Land and groove recording is effective in boosting track density, because it basically doubles the track density ensured solely by groove recording or by land recording. In particular, implementing a land and groove recording scheme provides high track density without reducing the diameter of the laser beam spot used to record or reproduce data.
The so-called Magnetically Induced Super Resolution (MSR) technology has been found effective as a magneto-optical recording medium-oriented technique intended for mass data storage on the magneto-optical disc in terms of track direction density. Some magneto-optical recording media, such as domain wall displacement detection media and magnetic amplifying magneto-optical system media, permit a huge increase in linear recording density without being limited theoretically by wavelength parameters of an optical system in use or by the numerical aperture (NA) of an objective lens incorporated.
Generally, however, attempts to boost track density in the land and groove recording setup tend to narrow the allowable range of laser power levels at the time of recording. That is because data signals held illustratively in grooves can be deleted accidentally while data are being recorded to lands. In particular, where the above-mentioned domain wall displacement detection medium or magnetic amplifying magneto-optical system medium is used, the allowable range of laser power levels for recording is considerably limited.
The reduced margins of laser power require that laser power levels be controlled within correspondingly narrow ranges. That in turn makes it necessary to minimize deviations between individual recording media manufactured, differences between individual optical parts, and fluctuations in ambient temperature and humidity. These requirements entail increased manufacturing costs and a decline in production efficiency. Since there are numerous cases where the dependency on laser power at the time of recording or reproduction varies between lands and grooves, implementation of a stable optical disc system requires very complicated control schemes.